<p> Unit 1-6 RETEACHING GALAXIES Vocabulary to Know:</p><p>Measuring Distances • Light Year – The distance light travels in one year. • Light travels at 186,000 miles/sec or 671 million (6.71×108) miles/hour • It takes 8.4 minutes for light to travel to the Earth</p><p>Galaxies • A galaxy is a system of millions or billions of stars, made of gas and dust, held together by gravitational attraction. • Galaxies are different sizes and shapes. • How far is it across our own galaxy? 100,000 light years • How many stars are in the Milky Way? 200,000,000,000 stars</p><p>Spiral/Disk Galaxy • Spiral or disk shaped • Has ‘arms’ • Dense center • We live in a spiral galaxy called the Milky Way. • Our Sun is located about 2/3 of the way out on one of the arms.</p><p>Elliptical Galaxy • Oval-shaped • Most abundant galaxies in the universe • Most are composed of older, low-mass stars</p><p>Irregular Galaxy • No defined shape • No clear bulge or disk • The leftovers of two colliding galaxies Sources: http://www.kidsastronomy.com/galaxys.htm</p>